Enzymatic production of (meth)acrylic acid esters

ABSTRACT

A method for the production of partially esterified (meth)acrylic acid esters of polyalcohols and the use thereof.

The present invention relates to a process for preparing partial(meth)acrylic esters of polyalcohols and to their use.

(Meth)acrylic esters are generally prepared by acid- or base-catalyzedesterification of (meth)acrylic acid or transesterification of other(meth)acrylic esters with alcohols.

Partial (meth)acrylic esters generally cannot be prepared specificallyby an esterification or transesterification, since statistical mixturesare obtained.

When acetal- or ketal-protected polyalcohols are being used anacid-catalyzed process for their preparation is no longer possible,since acetal and ketal groups are acid-labile.

In the case of base-catalyzed transesterification or other syntheses theproducts are often complex mixtures which are occasionally colored. Inorder to remove coloration and unconverted reactants it is necessary towork up the product mixtures by means of costly and inconvenientalkaline washes.

U.S. Pat. No. 2,680,735 describes the preparaton of (meth)acrylic estersof acetal- and ketal-protected glycerol by a transesterification of theacetal- and ketal-protected glycerol with lower (meth)acrylic esters attemperatures above 70° C. with catalysis by alkali metal oxides, sodiummethoxide or sodium ethoxide.

R. Deschenaux and J. K. Stille describe the same reaction in J. Org.Chem., 1985, 50, 2299-2302, using titanium tetraisopropoxide ascatalyst, with subsequent acidic cleavage of the ketal protectivegroups.

A disadvantage of this preparation variant is the possibility ofcolorations of the reaction mixture when metal catalysts are used.

JP 2001-294 555 (CA No. 135:303 607) and JP 2001-294 554 (CA No. 135:303606) describe the preparation of glyceryl monomethacrylate by reactionof methacrylic acid with glycidol (2,3-epoxy-1-propanol).

Disadvantages there are the yield of not more than 80% and the lowpurity of 95%.

JP 08-277 245 (CA No. 126:31792) describes the preparation of glycerylmono-(meth)acrylate by hydrolysis of glycidyl (meth)acrylate.

A disadvantage of these synthesis routes, however, is the involvement ofhighly reactive and toxic epoxides.

The preparation of (meth)acrylic esters by an enzymatic esterificationor transesterification is known.

Kumar and Gross describe in J. Am. Chem. Soc. 2002, 124, 1850-1851 thelipase-catalyzed reaction of isopropylidene-protected sugars by reactionwith vinyl methacrylate. Complete reaction is achieved by means of thespecific reactant, vinyl methacrylate, since vinyl alcohol liberated iswithdrawn from the reaction equilibrium as acetaldehyde. A disadvantageof this process is that vinyl methacrylate is not commerciallyavailable.

A. T. J. W. de Goede et al. describe in Biocatalysis, 1994, 9, 145-155the transesterification of α-O-octylglucoside with ethyl acrylate toform the 6-O-acrylic ester in the presence of lipases. Disadvantages ofthis process are that it is restricted to glucosides and glycosidicbonds and reacts sensitively to steric influences in the glucoside.Moreover, products with relatively high degrees of acrylicization areobtained due to unselective side reactions.

EP-A1 999 229 describes the enzymatic esterification andtransesterification of polyoxyalkylenes.

Hajjar et al. describe in Biotechnol. Lett. 1990, 12, 825-830 theenzymatic transesterification of cyclic and open-chain alkanediols withethyl acrylate with a lipase from Chromobacterium viscosum. Thereactions proceed with an 18-fold molar excess of the alkyl acrylateover the diol in a solvent-free system. This produces mixtures ofmonoacrylates and diacrylates.

U.S. Pat. No. 5,240,835 describes the transesterification of alkylacrylates with alcohols under catalysis by a biocatalyst fromCorynebacterium oxydans. Exemplified therein is the reaction of a96-fold molar excess of ethyl acrylate with2,2-dimethyl-1,3-propanediol. The yield, after 3 days at 30° C., wasonly 21%.

It is an object of the present invention to provide a further processwith which partial (meth)acrylic esters of polyalcohols can be preparedin high conversions and with high purities from simple reactants. Thesynthesis ought to proceed under mild conditions, giving products havinga low color number and high purity.

We have found that this object is achieved by a process for preparingpartial (meth)acrylic esters by subjecting polyalcohols (C) in which atleast two hydroxyl groups together are joined in an acetal group orketal group to esterification with (meth)acrylic acid or totransesterification with at least one (meth)acrylic ester (D) in thepresence of at least one enzyme (E).

By means of the process of the invention it is possible to preparepartial (meth)acrylic esters (F) in high chemical and space/time yieldand under mild conditions with good color numbers.

(Meth)acrylic acid in this text stands for methacrylic acid and acrylicacid, preferably for acrylic acid.

Polyalcohols (C) useful in accordance with the invention are thosecompounds which comprise at least one acetal group or ketal group,preferably from 1 to 5, more preferably from 1 to 3, very preferably 1or 2, and in particular one acetal or ketal group, and at least onehydroxyl group (—OH), preferably from 1 to 10, more preferably from 1 to6, very preferably from 1 to 3, in particular 1 or 2, and especially onehydroxyl group.

In the acetal groups and ketal groups of the polyalcohols (C) 2 hydroxylgroups of the polyols (B) on which the polyalcohols (C) are based are ineach case joined together.

Preferred polyalcohols (C) are those obtainable by

(a) reacting an aldehyde or ketone (A) with a polyol (B) and

(b) where appropriate, purifying the reaction mixture obtainable froma).

Aldehydes or ketones (A) are of the formula IR¹—C(═O)—R²  (I),where

R¹ and R² independently of one another are hydrogen, C₁-C₁₈ alkyl,C₂-C₁₈ alkyl uninterrupted or interrupted by one or more oxygen and/orsulfur atoms and/or by one or more substituted or unsubstituted iminogroups, or are C₂-C₁₈ alkenyl, C₆-C₁₂ aryl, C₅-C₁₂ cycloalkyl or a five-or six-membered, oxygen, nitrogen and/or sulfur-containing heterocycle,it being possible for the specified radicals to be substituted in eachcase by aryl, alkyl, aryloxy, alkyloxy, heteroatoms and/or heterocyclesor for R¹ and R² together with the carbonyl carbon to form a four- totwelve-membered ring.

Examples of R¹ and/or R² are hydrogen, methyl, ethyl, iso-propyl,n-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-hexyl, n-heptyl,n-octyl, n-decyl, n-dodecyl, n-tetradecyl, n-hexadecyl, n-octadecyl,2-ethylhexyl, cyclopentyl, cyclohexyl, cyclooctyl, cyclododecyl, phenylor naphthyl, preference being given to hydrogen, methyl, and phenyl, andparticular preference to methyl.

Examples of aldehydes and ketones (A) are formaldehyde, acetaldehyde,propionaldehyde, n-butyraldehyde, isobutyraldehyde, pivaldehyde,benzaldehyde, acetone, methyl ethyl ketone, diethyl ketone,acetophenone, benzophenone, cyclopentanone, cyclohexanone orcyclododecanone, preference being given to formaldehyde, acetaldehyde,pivaldehyde, acetone, methyl ethyl, ketone, diethyl ketone,cyclopentanone or cyclohexanone, particular preference to formaldehyde,acetone or cyclopentanone, and very particular preference to acetone.

Polyols (B) are polyols having from 3 to 10 hydroxyl groups, preferablyfrom 3 to 6.

Examples of polyols (B) are glycerol, diglycerol, trimethylolbutane,trimethylolpropane, ditrimethylolpropane, trimethylolethane,pentaerythritol, dipentaerythritol, sorbitol, mannitol, diglycerol,threitol, erythritol, adonitol (ribitol), arabitol (lyxitol), xylitol,dulcitol (galactitol), maltitol or isomalt. Preference is given tosorbitol, glycerol, diglycerol, trimethylolpropane,ditrimethylolpropane, trimethylolethane, and pentaerythritol, particularpreference to glycerol, trimethylolpropane, and pentaerythritol, andvery particular preference to glycerol.

The reaction of an aldehyde or ketone (A) with a polyol (B) is known perse, is not restricted, and can take place, for example, as described inOrganikum, VEB Deutscher Verlag der Wissenschaften, 17th edition, Berlin1988, p. 398.

Typically the aldehyde/ketone (A) and the polyol (B) are reacted withone another in a stoichiometry of from 0.7 to 1.2 mol (A): 2 molhydroxyl groups in (B) that are to be protected, preferably 0.8-1.2:2,more preferably 0.9-1.1:2, very preferably 0.95-1.1:2, and in particular1:2 mol/mol.

The reaction takes place in general at a temperature of from 0 to 120°C., in particular from 20 to 100° C., more preferably from 30 to 80° C.,and very preferably from 40 to 80° C.

The reaction is generally at an end within 12 hours, preferably withinfrom 15 minutes to 10 hours, more preferably in 30 minutes to 8 hours,very preferably from 45 minutes to 6 hours, and in particular withinfrom 1 to 4 hours.

The acetalization/ketalization takes place in general with acidcatalysis, catalyzed for example by mineral acids, such as hydrochloricacid, sulfuric acid, nitric acid, or phosphoric acid, for example,para-toluenesulfonic acid, benzenesulfonic acid, methanesulfonic acid,trifluoromethanesulfonic acid, mineral clays or acidic ion exchangers,or catalyzed by enzymes.

The reaction can be conducted without solvent or preferably in thepresence of a solvent, examples being ethers and hydrocarbons, includinghalogenated hydrocarbons.

The acetalization/ketalization is conducted preferably with removal ofthe water liberated during the reaction, in the presence for example ofmolecular sieve or zeolites or by membrane separation, or, withparticular preference, with azeotropic removal of water by a solventwhich forms an azeotrope with water.

The acetalization/ketalization can take place with particular preferenceas described in DE-A1 196 47 395, and especially from page 2 line 55 topage 4 line 20 therein, the disclosure content of which is herebyincorporated expressly by reference.

In a further step b), if desired, the reaction mixture obtainable froma) can be purified, by means for example of filtration, distillation,rectification, chromatography, treatment with ion exchangers,adsorbents, neutral, acidic and/or alkaline washing, stripping orcrystallization.

Examples of the acetal- or ketal-protected polyalcohols (C) useful inaccordance with the invention are therefore those polyalcoholspreparable by protecting the polyols (B) with aldehydes or ketones (A).

These are, with particular preference, polyalcohols (C) containing a1,3-dioxolane or 1,3-dioxane structure which is monosubstituted ordisubstituted in position 2, especially those containing a2,2-dimethyl-1,3-dioxolane or 2,2-dimethyl-1,3-dioxane structure.

Particularly preferred polyalcohols (C) are4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane,4-hydroxymethyl-2-methyl-1,3-dioxolane,4-hydroxymethyl-2,2-diethyl-1,3-dioxolane,4-hydroxymethyl-2-tert-butyl-1,3-dioxolane,4-hydroxymethyl-2-phenyl-1,3-dioxolane,5-ethyl-5-hydroxymethyl-2,2-dimethyl-1,3-dioxane,5-ethyl-5-hydroxymethyl-2-methyl-1,3-dioxane,5-ethyl-5-hydroxymethyl-2,2-diethyl-1,3-dioxane,5-ethyl-5-hydroxy-methyl-2-tert-butyl-1,3-dioxane,5-ethyl-5-hydroxymethyl-2-phenyl-1,3-dioxane,1,2-O-isopropylidene-α-D-glucofuranose, 2,3-O-isopropylidene-threitol(=2,2-dimethyl-1,3-dioxolane-4,5-dimethanol), and5,5-bis(hydroxymethyl)-2,2-dimethyl-1,3-dioxane. A further example is5-ethyl-5-hydroxymethyl-1,3-dioxane.

Step c) is the esterification with (meth)acrylic acid or, preferably,the transesterification of the acetal- or ketal-protected polyalcohol(C) with at least one, preferably one, (meth)acrylate (D) in thepresence of at least one, preferably one, enzyme (E) that catalyzes thetransesterification.

Compounds (D) can be (meth)acrylic acid or esters of (meth)acrylic acidwith a saturated alcohol, preferably saturated C₁-C₁₀ alkyl esters of(meth)acrylic acid, more preferably saturated C₁-C₄ alkyl esters of(meth)acrylic acid.

Saturated for the purposes of this text means compounds without multipleC—C bonds (except of course for the C═C double bond in the (meth)acrylicunits).

Examples of compounds (D) are methyl, ethyl, n-butyl, iso-butyl,n-octyl, and 2-ethylhexyl (meth)acrylate, 1,2-ethylene glycol di- andmono(meth)acrylate, 1,4-butanediol di- and mono(meth)acrylate,1,6-hexanediol di- and mono(meth)acrylate, trimethylolpropanetri(meth)acrylate, and pentaerythritol tetra(meth)acrylate.

Particular preference is given to methyl, ethyl, n-butyl, and2-ethylhexyl (meth)acrylate and very particular preference to methyl,ethyl, and n-butyl (meth)acrylate.

The enzymatic esterification or transesterification with a(meth)acrylate takes place in general at from 0 to 100° C., preferablyfrom 20 to 80° C., more preferably from 20 to 70° C., and verypreferably from 20 to 60° C.

Examples of enzymes (E) useful in accordance with the invention arethose selected from hydrolases (E.C. 3.-.-.-), and among theseespecially from the esterases (E.C. 3.1.-.-), lipases (E.C. 3.1.1.3),glycosylases (E.C. 3.2.-.-), and proteases (E.C. 3.4.-.-), in free formor in a form in which they are chemically or physically immobilized on acarrier, preferably lipases, esterases or proteases, and more preferablyesterases (E.C. 3.1.-.-). Very particular preference is given toNovozyme 435 (Lipase from Candida antarctica B) or lipase fromAspergillus sp., Aspergillus niger sp., Mucor sp., Penicillium cyclopiumsp., Geotricum candidum sp., Rhizopus javanicus, Burkholderia sp.,Candida sp., Pseudomonas sp., or porcine pancreas, and especialpreference to lipase from Candida antarctica B or from Burkholderia sp.

The enzyme content of the reaction medium is generally in the range fromabout 0.1 to 10% by weight, based on the sum of components (C) and (D)employed.

The reaction time depends among other things on the temperature, on theamount of the enzyme catalyst used and its activity, and on the requiredconversion, and also on the partly esterified alcohol. The reaction timeis preferably adapted so that the conversion of all hydroxyl functionsoriginally present in the alcohol (C) is at least 70%, preferably atleast 80%, more preferably at least 90%, very preferably at least 95%,and in particular at least 97%. The time sufficient for this isgenerally from 1 to 48 hours, preferably from 1 to 12 hours, and morepreferably from 1 to 6 hours.

The molar ratio of (meth)acrylic acid compound (D) (based on the(meth)acrylic units) to partly esterified alcohol (C) (based on hydroxylgroups) can vary within a wide range, such as in a ratio, for example,of from 100:1 to 1:1, preferably from 50:1 to 1:1, more preferably from20:1 to 1:1, and very preferably from 10:1 to 1:1.

The reaction can proceed in organic solvents or mixtures thereof orwithout the addition of solvents. The batches are generallysubstantially free of water (i.e., less than 10%, preferably less than5%, more preferably less than 1%, and very preferably less than 0.5% byvolume of water added).

Suitable organic solvents are those known for these purposes, examplesbeing tertiary monools, such as C₃-C₆ alcohols, preferably tert-butanol,tert-amyl alcohol, pyridine, poly-C₁-C₄ alkylene glycol di-C₁-C₄ alkylethers, preferably polyethylene glycol di-C₁-C₄ alkyl ethers, such as1,2-dimethoxyethane, diethylene glycol dimethyl ether, polyethyleneglycol dimethyl ether 500, C₁-C₄ alkylene carbonates, especiallypropylene carbonate, C₃-C₆ alkyl acetates, especially tert-butylacetate, THF, toluene, 1,3-dioxolane, acetone, iso-butyl methyl ketone,ethyl methyl ketone, 1,4-dioxane, tert-butyl methyl ether, cyclohexane,methylcyclohexane, toluene, hexane, dimethoxymethane,1,1-dimethoxyethane, acetonitrile, and single-phase or multiphasemixtures thereof. It can be advantageous to separate alcohol or waterthat is liberated by means of a binary or ternary heteroazeotrope whichboils as close as possible to the temperature optimum of the enzymeused. The alcohol removed in this way can then be removed by phaseseparation or membrane vapor separation.

As an option it is possible to add aqueous solvents to the organicsolvents, thereby producing single-phase or multi-phase reactionsolutions, depending on the organic solvent. Examples of aqueoussolvents are water and also aqueous, dilute (e.g., 10 to 100 mM)buffers, with a pH for example in the range from about 6 to 8, such aspotassium phosphate buffer or TRIS-HCl buffer, for example.

The water fraction in the reaction mixture is generally 0-10% by volume.The reactants are preferably used without pretreatment (drying, waterdoping).

The substrates are either in solution, in suspension as solids, or inemulsion in the reaction medium. The initial concentration of thereactants is preferably in the range from about 0.1 to 20 mol/l, inparticular from 0.15 to 10 mol/I or from 0.2 to 5 mol/l.

The reaction can take place continuously, in a tube reactor or in astirred reactor cascade, for example, or batchwise.

The reaction can be conducted in all reactors suitable for suchreactions. Reactors of this kind are known to the skilled worker. Thereaction preferably takes place in a stirred tank reactor or fixed bedreactor.

The reaction mixture can be mixed using any desired methods. There is noneed for special stirring apparatus. The reaction medium can be a singlephase or a plurality of phases and the reactants are dissolved,suspended or emulsified therein, charged to the reaction vessel togetherwhere appropriate with molecular sieve, and admixed with the enzymepreparation at the start of the reaction and also, where appropriate,one or more times during the course of the reaction. The temperatureduring the reaction is adjusted to the desired level and can, ifdesired, be raised or lowered during the course of the reaction.

Where the reaction is carried out in a fixed bed reactor, said reactoris preferably packed with immobilized enzymes, the reaction mixturebeing pumped through a column packed with the enzyme. It is alsopossible to carry out the reaction in a fluidized bed, in which case theenzyme is used in a form in which it is immobilized on a carrier. Thereaction mixture can be pumped continuously through the column, with theresidence time and hence the desired conversion being controllable bymeans of the flow rate. It is also possible to pump the reaction mixturein circulation through a column, with the possibility also ofdistillative removal of the alcohol that is liberated at the same time,under reduced pressure.

The removal of water in the case of an esterification, or of alcoholsreleased in a transesterification from the alkyl (meth)acrylates, takesplace continuously or gradually in a manner known per se, by means ofreduced pressure, azeotropic removal, absorption, pervaporation, anddiffusion over membranes, for example.

Suitable for this purpose are, preferably, molecular sieves or zeolites(with a pore size, for example, in the range of about 3-10 angstroms),distillative separation or separation using appropriate semipermeablemembranes.

Yet another possibility is to pass the isolated mixture of alkyl(meth)acrylate and its parent alcohol, said mixture frequently formingan azeotrope, directly to a plant for the preparation of the alkyl(meth)acrylate, so as to reuse it therein in an esterification with(meth)acrylic acid.

After the end of the reaction the reaction mixture obtainable from c)can be used further without further purification or, if required, can bepurified in a further step d).

d) Generally the enzyme used is just separated off from the reactionmixture and the reaction product is freed from any organic solvent used.

The enzyme is separated off generally by filtration, absorption,centrifugation or decanting. The enzyme separated off can subsequentlybe used for further reactions.

Removal of the organic solvent takes place generally by distillation,rectification or, in the case of solid reaction products, by filtration.

For the further purification of the reaction product it is also possibleto carry out a chromatography.

Preferably in step d), however, just the enzyme used and any solventused are separated off.

The reaction conditions in the enzymatic esterification ortransesterification are mild. The low temperatures and other mildconditions prevent the formation of by-products in step c), which mightotherwise originate, for example, from chemical catalysts or as a resultof unwanted free-radical polymerization of the (meth)acrylate used,which can otherwise be prevented only by adding stabilizers. In thereaction regime of the invention it is possible to add additionalstabilizer to the (meth)acrylic compound (D) over and above the storagestabilizer present in any case, examples of such additional stabilizersincluding hydroquinone monomethyl ether, phenothiazine, phenols, such as2-tert-butyl-4-methylphenol or 6-tert-butyl-2,4-dimethyl-phenol, forexample, or N-oxyls, such as4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, and4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl, in amounts for example offrom 50 to 2000 ppm. The transesterification or esterification isadvantageously conducted in the presence of an oxygenous gas, preferablyair or air/nitrogen mixtures. Additionally the enzyme catalyst can beremoved without problems from the end product. Additionally there isgenerally no substantial cleavage of the acetal groups or ketal groupsby enzymatic hydrolysis; the proportion of by-products is generally lessthan 10%, preferably less than 5%.

The acetal- and/or ketal-protected (meth)acrylic esters obtainable fromstages c) or d) can be used as such, but are preferably deprotected in astage e) and, where appropriate, purified in a stage f).

The cleavage in stage e) generally takes place under acid catalysis andwith addition of water, and is known per se and not restricted.

The reaction takes place in general at a temperature of from 20 to 150°C., in particular at from 40 to 120° C., and very preferably at from 50to 100° C.

The reaction is generally over within 12 hours, preferably from within15 minutes to 10 hours, more preferably in 30 minutes to 8 hours, verypreferably from 45 minutes to 6 hours, and in particular within from 1to 4 hours.

The cleavage of the acetals/ketals generally takes place under acidcatalysis, catalyzed for example by mineral acids, such as hydrochloricacid, sulfuric acid, nitric acid or phosphoric acid,para-toluenesulfonic acid, benzenesulfonic acid, methanesulfonic acid,trifluoromethanesulfonic acid, mineral clays, acidic ion exchangers orcatalyzed by enzymes, with the addition of up to 20%, preferably up to15%, and more preferably up to 10% by weight of water.

The reaction can be conducted without solvent or in preferred presenceof such a solvent, examples of which include ethers, alcohols,hydrocarbons, ketones, halogenated hydrocarbons, and water.

The cleavage can be conducted preferably as described in WO 00/63149, inparticular from page 4 line 28 to page 18 line 24 therein and theexamples, WO 00/63150, particularly from page 5 line 12 to page 16 line30 therein and the examples, and in DE-A1 101 18 232, particularly frompage 3 line 49 to page 4 line 32 therein and the examples, thedisclosure content of these three publications hereby being expresslyincorporated by reference.

The reaction mixture obtainable from e) can be purified if desired in afurther step f), purification taking place for example by filtration,distillation, rectification, chromatography, treatment with ionexchangers, adsorbents, neutral, acidic and/or alkaline washing,stripping or crystallization.

The acetal- and/or ketal-protected (meth)acrylic esters obtainable fromstages c) and d), or the partial (meth)acrylic esters (F) obtainablefrom steps e) and f), can be used with advantage as monomers orcomonomers in poly(meth)acrylates or as reactive diluents inradiation-curable and/or dual-cure poly(meth)acrylates.Poly(meth)acrylates of this kind are suitable, for example, as bindersin radiation-curable or dual-cure coating compositions. Additionally thepartial (meth)acrylic esters (F) can be used in polyurethanes, such asin PU dispersions, PU foams, PU adhesives, and PU coatings, for example.

Coatings thus obtainable have very high scratch resistance, hardness,chemical resistance, elasticity, and adhesion, on both hydrophilic andhydrophobic substrates.

The present invention accordingly further provides for the use of theacetal-/ketal-protected or partial (meth)acrylic esters prepared by theprocess of the invention as reactive diluents or binders inradiation-curable or dual-cure coating materials, preferably intopcoats, more preferably in transparent clearcoat materials. Thepartial (meth)acrylic esters prepared in accordance with the inventioncan of course also be used as monomers in polymerizations, togetherwhere appropriate with other polymerizable monomers, such as(meth)acrylic acid, (meth)acrylic esters, styrene, butadiene,acrylonitrile, vinyl acetate, N-vinylpyrrolidone, 4-hydroxybutyl vinylether or N-vinylformamide, for example.

“Dual cure” means that the coating materials are curable thermally andwith actinic radiation. Actinic radiation for the purposes of thepresent invention means electromagnetic radiation such as visible light,UV radiation or X-rays, especially UV radiation, and corpuscularradiation such as electron beams.

Radiation-curable binders are those which can be cured by means ofactinic radiation as defined above, in particular by means of UVradiation.

The present invention further provides coating formulations comprisingthe acetal-/ketal-protected or partial (meth)acrylic esters obtainableby the process of the invention. The partial (meth)acrylic esters can beused both in basecoat and in topcoat materials. In view of theirparticular properties, such as the raising of the scratch resistance andelasticity, and the lowering of the viscosity, particularly in the caseof branched polyacrylates, of a radiation-cured clearcoat, their use intopcoats is preferred.

Besides the partial (meth)acrylic esters (F) obtainable by the processof the invention a radiation-curable composition of the invention maycomprise the following components:

(G) at least one polymerizable compound having two or morecopolymerizable, ethylenically unsaturated groups,

(H) if desired, reactive diluents,

(I) if desired, photoinitiator, and

(J) if desired, further, typical coatings additives.

Suitable compounds (G) include radiation-curable, free-radicallypolymerizable compounds having a plurality of, i.e., at least two,copolymerizable, ethylenically unsaturated groups.

Compounds (G) are preferably vinyl ether compounds or (meth)acrylatecompounds, particular preference being given in each case to theacrylate compounds, i.e., to the derivatives of acrylic acid.

Preferred vinyl ether and (meth)acrylate compounds (G) contain from 2 to20, preferably from 2 to 10, and very preferably from 2 to 6copolymerizable, ethylenically unsaturated double bonds.

Particular preference is given to such compounds (G) having anethylenically unsaturated double bond content of 0.1-0.7 mol/100 g, verypreferably 0.2-0.6 mol/100 g.

The number-average molecular weight M_(n) of the compounds (G), unlessotherwise specified, is preferably below 15 000, more preferably 300-12000, very preferably from 400 to 5000, and in particular 500-3000 g/mol(as determined by gel permeation chromatography using polystyrenestandards and tetrahydrofuran as eluent).

As (meth)acrylate compounds mention may be made of (meth)acrylic estersand especially acrylic esters and also of vinyl ethers of polyfunctionalalcohols, especially those which other than the hydroxyl groups compriseno functional groups or, if any at all, contain ether groups. Examplesof such alcohols include bifunctional alcohols, such as ethylene glycol,propylene glycol and their counterparts with higher degrees ofcondensation, such as diethylene glycol, triethylene glycol, dipropyleneglycol, tripropylene glycol etc., 1,2-, 1,3- or 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentylglycol, alkoxylated phenolic compounds, such as ethoxylated and/orpropoxylated bisphenols, 1,2-, 1,3- or 1,4-cyclohexanedimethanol,alcohols with a functionality of three or more, such as glycerol,trimethylolpropane, butanetriol, trimethylolethane, pentaerythritol,ditrimethylolpropane, dipentaerythritol, sorbitol, mannitol, and thecorresponding alkoxylated alcohols, especially ethoxylated and/orpropoxylated alcohols.

The alkoxylation products are obtainable conventionally by reacting theabove alcohols with alkylene oxides, especially ethylene oxide orpropylene oxide. The degree of alkoxylation per hydroxyl group ispreferably from 0 to 10, i.e., 1 mol of hydroxyl group may have beenalkoxylated with up to 10 mol of alkylene oxides.

As (meth)acrylate compounds mention may further be made of polyester(meth)acrylates, which are the (meth)acrylic esters or vinyl ethers ofpolyesterols, and also of urethane, epoxy or melamine (meth)acrylates.

Urethane (meth)acrylates, for example, are obtainable by reactingpolyisocyanates with hydroxyalkyl (meth)acrylates and, whereappropriate, chain extenders such as diols, polyols, diamines,polyamines, or dithiols or polythiols.

The urethane (meth)acrylates preferably have a number-average molarweight M_(n) of from 500 to 20 000, in particular from 750 to 10 000,and more preferably from 750 to 3000 g/mol (as determined by gelpermeation chromatography using polystyrene standards).

The urethane (meth)acrylates preferably comprise from 1 to 5, morepreferably from 2 to 4, mol of (meth)acrylic groups per 1000 g ofurethane (meth)acrylate.

Epoxy (meth)acrylates are obtainable by reacting epoxides with(meth)acrylic acid. Examples of suitable epoxides include epoxidizedolefins or glycidyl ethers, e.g. bisphenol A diglycidyl ether oraliphatic glycidyl ethers, such as butanediol diglycidyl ether.

Melamine (meth)acrylates are obtainable by reacting melamine with(meth)acrylic acid or the esters thereof.

The epoxy (meth)acrylates and melamine (meth)acrylates preferably have anumber-average molar weight M_(n) of from 500 to 20 000, more preferablyfrom 750 to 10 000 g/mol and very preferably from 750 to 3000 g/mol; theamount of (meth)acrylic groups is preferably from 1 to 5, morepreferably from 2 to 4, per 1000 g of epoxy (meth)acrylate or melamine(meth)acrylate (as determined by gel permeation chromatography usingpolystyrene standards and tetrahydrofuran as eluent).

Also suitable are carbonate (meth)acrylates, comprising on averagepreferably from 1 to 5, in particular from 2 to 4, more preferably 2 or3 (meth)acrylic groups and, with very particular preference, 2(meth)acrylic groups.

The number-average molecular weight M_(n) of the carbonate(meth)acrylates is preferably less than 3000 g/mol, more preferably lessthan 1500 g/mol, very preferably less than 800 g/mol (as determined bygel permeation chromatography using polystyrene standards andtetrahydrofuran as mobile phase).

The carbonate (meth)acrylates are readily obtainable bytransesterification of carbonic esters with polyhydric, preferablydihydric, alcohols (diols, e.g. hexanediol) and subsequentesterification of the free OH groups with (meth)acrylic acid or elsetransesterification with (meth)acrylic esters, as described for examplein EP-A 92 269. They are also obtainable by reacting phosgene, ureaderivatives with polyhydric alcohols, e.g. dihydric alcohols.

Suitable reactive diluents (compounds (H)) include radiation-curable,free-radically or cationically polymerizable compounds having only oneethylenically unsaturated co-polymerizable group.

Examples that may be mentioned include C₁-C₂₀ alkyl (meth)acrylates,vinylaromatics having up to 20 carbon atoms, vinyl esters of carboxylicacids comprising up to 20 carbon atoms, ethylenically unsaturatednitriles, vinyl ethers of alcohols comprising 1 to 10 carbon atoms,α,β-unsaturated carboxylic acids and their anhydrides, and aliphatichydrocarbons having from 2 to 8 carbon atoms and 1 or 2 double bonds.

Preferred alkyl (meth)acrylates are those with a C₁-C₁₀ alkyl radical,such as methyl methacrylate, methyl acrylate, n-butyl acrylate, ethylacrylate, and 2-ethylhexyl acrylate.

In particular, mixtures of the alkyl (meth)acrylates are also suitable.

Examples of vinyl esters of carboxylic acids having 1 to 20 carbon atomsare vinyl laurate, vinyl stearate, vinyl propionate, and vinyl acetate.

Examples of α,β-unsaturated carboxylic acids and their anhydridesinclude acrylic acid, methacrylic acid, fumaric acid, crotonic acid,itaconic acid, maleic acid, and maleic anhydride, preferably acrylicacid.

Examples of suitable vinylaromatic compounds include vinyltoluene,α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, and, preferably,styrene.

Examples of nitriles are acrylonitrile and methacrylonitrile.

Examples of suitable vinyl ethers include vinyl methyl ether, vinylisobutyl ether, vinyl hexyl ether, and vinyl octyl ether.

As nonaromatic hydrocarbons having 2 to 8 carbon atoms and one or twoolefinic double bonds mention may be made of butadiene, isoprene, and ofethylene, propylene, and isobutylene.

It is further possible to employ N-vinylformamide, N-vinylpyrrolidone,and N-vinylcaprolactam.

As photoinitiator (I) it is possible to use photoinitiators known to theskilled worker, examples being those in “Advances in Polymer Science”,Volume 14, Springer Berlin 1974 or in K. K. Dietliker, Chemistry andTechnology of UV- and EB-Formulation for Coatings, Inks and Paints,Volume 3; Photoinitiators for Free Radical and Cationic Polymerization,P. K. T. Oldring (ed.), SITA Technology Ltd, London.

Suitable examples include mono- or bisacylphosphine oxides such asIrgacure 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide), asdescribed for example in EP-A 7 508, EP-A 57 474, DE-A 196 18 720, EP-A495 751 or EP-A 615 980, examples being2,4,6-trimethylbenzoyidiphenylphosphine oxide (Lucirin® TPO), ethyl2,4,6-trimethylbenzoylphenylphosphinate, benzophenones,hydroxyacetophenones, phenylglyoxylic acid and derivatives thereof, ormixtures of these photoinitiators.

Examples that may be mentioned include benzophenone, acetophenone,acetonaphthoquinone, methyl ethyl ketone, valerophenone, hexanophenone,α-phenylbutyrophenone, p-morpholinopropiophenone, dibenzosuberone,4-morpholinobenzophenone, 4-morpholinodeoxybenzoin, p-diacetylbenzene,4-aminobenzophenone, 4′-methoxyacetophenone, β-methylanthraquinone,tert-butylanthraquinone, anthraquinonecarboxylic esters, benzaldehyde,α-tetralone, 9-acetylphenanthrene, 2-acetylphenanthrene,10-thioxanthenone, 3-acetylphenanthrene, 3-acetylindole, 9-fluorenone,1-indanone, 1,3,4-triacetylbenzene, thioxanthen-9-one, xanthen-9-one,2,4-dimethylthioxanthone, 2,4-diethylthioxanthone,2,4-diisopropylthioxanthone, 2,4dichlorothioxanthone, benzoin, benzoinisobutyl ether, chloroxanthenone, benzoin tetrahydropyranyl ether,benzoin methyl ether, benzoin ethyl ether, benzoin butyl ether, benzoinisopropyl ether, 7H-benzoin methyl ether, benz[de]anthracen-7-one,1-naphthaldehyde, 4,4′-bis(dimethylamino)benzophenone,4-phenylbenzophenone, 4-chlorobenzophenone, Michler's ketone,1-acetonaphthone, 2-acetonaphthone, 1-benzoylcyclohexan-1-ol,2-hydroxy-2,2-dimethylacetophenone, 2,2-dimethoxy-2-phenylacetophenone,2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone,1-hydroxyacetophenone, acetophenone dimethyl ketal,o-methoxybenzophenone, triphenylphosphine, tri-o-tolylphosphine,benz[a]anthracene-7,12-dione, 2,2-diethoxyacetophenone, benzil ketals,such as benzil dimethyl ketal,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one,anthraquinones such as 2-methylanthraquinone, 2-ethylanthraquinone,2-tert-butylanthraquinone, 1-chloroanthraquinone, 2-amylanthraquinone,and 2,3-butanedione.

Also suitable are nonyellowing or low-yellowing photoinitiators of thephenylglyoxalic ester type, as described in DE-A 198 26 712, DE-A 199 13353 or WO 98/33761.

Among said photoinitiators phosphine oxides, α-hydroxy ketones andbenzophenones are preferred.

In particular it is also possible to use mixtures of differentphotoinitiators.

The photoinitiators can be used alone or in combination with aphotopolymerization promoter, of the benzoic acid, amine or similartype, for example.

As further, typical coatings additives (J) it is possible to make use,for example, of anti-oxidants, oxidation inhibitors, stabilizers,activators (accelerators), fillers, pigments, dyes, devolatilizers,luster agents, antistats, flame retardants, thickeners, thixotropicagents, leveling assistants, binders, antifoams, fragrances,surfactants, viscosity modifiers, plasticizers, tackifying resins(tackifiers), chelating agents or compatibilizers.

Examples of accelerators for thermo aftercure that can be used includetin octoate, zinc octoate, dibutyltin laurate, anddiazabicyclo[2.2.2]octane.

It is also possible to add one or more photochemically and/or thermallyactivatable initiators, such as potassium peroxodisulfate, dibenzoylperoxide, cyclohexanone peroxide, di-tert-butyl peroxide,azobisisobutyronitrile, cyclohexylsulfonyl acetyl peroxide, diisopropylpercarbonate, tert-butyl peroctoate or benzpinacol, and also, forexample, those thermally activatable initiators which have a half-lifeat 80° C. of more than 100 hours, such as di-t-butyl peroxide, cumenehydroperoxide, dicumyl peroxide, t-butyl perbenzoate, silylatedpinacols, available commercially, for example, under the trade nameADDID 600 from Wacker, or hydroxyl-containing amine N-oxides, such as2,2,6,6-tetramethylpiperidine-N-oxyl,4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl etc.

Further examples of suitable initiators are described in “PolymerHandbook”, 2nd ed., Wiley & Sons, New York.

Suitable thickeners besides free-radically (co)polymerized (co)polymersinclude customary organic and inorganic thickeners such ashydroxymethylcellulose or bentonites.

Examples of chelating agents which can be used includeethylenediamineacetic acid and salts thereof and also α-diketones.

Suitable fillers include silicates, examples being silicates obtainableby hydrolysis of silicon tetrachloride such as Aerosil® from Degussa,silicious earth, talc, aluminum silicates, magnesium silicates, calciumcarbonates, etc.

Suitable stabilizers include typical UV absorbers such as oxanilides,triazines, and benzotriazole (the latter obtainable as Tinuvin® gradesfrom Ciba-Spezialitätenchemie), and benzophenones. They can be usedalone or together with suitable free-radical scavengers, examples beingsterically hindered amines such as 2,2,6,6-tetramethylpiperidine,2,6-di-tert-butylpiperidine or derivatives thereof, e.g.,bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate. Stabilizers are normallyused in amounts of from 0.1 to 5.0% by weight, based on the solidcomponents present in the formulation.

Examples of stabilizers which are additionally suitable include N-oxyls,such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl,4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl,4-acetoxy-2,2,6,6-tetramethylpiperidine-N-oxyl,2,2,6,6-tetramethylpiperidine-N-oxyl,4,4′,4″-tris(2,2,6,6-tetramethylpiperidine-N-oxyl) phosphite or3-oxo-2,2,5,5-tetra-methylpyrrolidine-N-oxyl, phenols and naphthols,such as p-aminophenol, p-nitrosophenol, 2-tert-butylphenol,4-tert-butylphenol, 2,4-di-tert-butylphenol,2-methyl-4-tert-butylphenol, 4-methyl-2,6-tert-butylphenol(2,6-tert-butyl-p-cresol) or 4-tert-butyl-2,6-dimethylphenol, quinones,such as hydroquinone or hydroquinone monomethyl ether, aromatic amines,such as N,N-diphenylamine, N-nitrosodiphenylamine, phenylenediamines,such as N,N′-dialkyl-para-phenylenediamine, where the alkyl radicals canbe identical or different, consist independently of 1 to 4 carbon atoms,and be straight-chain or branched, hydroxylamines, such asN,N-diethylhydroxylamine, urea derivatives, such as urea or thiourea,phosphorus compounds, such as triphenyl-phosphine, triphenyl phosphiteor triethyl phosphite, or sulfur compounds, such as di-phenyl sulfide orphenothiazine, for example.

Examples of typical compositions for radiation-curable materials are:

-   -   (F) 20-100%, preferably 40-90%, more preferably 50-90%, and in        particular 60-80% by weight,    -   (G) 0-60%, preferably 5-50%, more preferably 10-40%, and in        partcular 10-30% by weight,    -   (H) 0-50%, preferably 5-40%, more preferably 6-30%, and in        particular 10-30% by weight,    -   (I) 0-20%, preferably 0.5-15%, more preferably 1-10%, and in        partcular 2-5% by weight, and    -   (J) 0-50%, preferably 2-40%, more preferably 3-30%, and in        particular 5-20% by weight,

with the proviso that (F), (G), (H), (I), and (J) together make 100% byweight.

The substrates are coated in accordance with methods which areconventional and are known to the skilled worker, applying at least onecoating material to the target substrate in the desired thickness andremoving any volatile constituents present in the coating material, withheating where appropriate. This operation can be repeated one or moretimes as desired. Application to the substrate may be made in a knownway, for example, by spraying, troweling, knifecoating, brushing,rolling, roller coating, flow coating, laminating, injection backmoldingor coextrusion. The coating thickness is generally in a range from about3 to 1000 g/m² and preferably from 10 to 200 g/m².

Further disclosed is a method of coating substrates which comprisesapplying the coating material to the substrate and drying it whereappropriate, curing it with electron beams or by UV exposure under anoxygenous atmosphere or, preferably, under inert gas, treating itthermally, if desired, at temperatures up to the level of the dryingtemperature, and then treating it thermally at temperatures of up to160° C., preferably between 60 and 160° C.

The method of coating substrates may also be conducted by following theapplication of the coating material first with thermal treatment attemperatures of up to 160° C., preferably between 60 and 160° C., andthen with curing using electron beams or by UV exposure under oxygen or,preferably, under inert gas.

Curing of the films formed on the substrate may take place by means ofheat alone if desired. Generally, however, the coatings are cured bothby exposure to high-energy radiation and thermally.

In addition to or instead of the thermal cure, curing may also takeplace by means of NIR radiation, which refers here to electromagneticradiation in the wavelength range from 760 nm to 2.5 μm, preferably from900 to 1500 nm.

Where two or more films of the coating composition are applied atop oneanother, it is possible for each coating operation to be followed by athermal, NIR and/or radiation cure.

Examples of suitable radiation sources for the radiation cure includelow-pressure, medium-pressure, and high-pressure mercury lamps,fluorescent tubes, pulsed lamps, metal halide lamps, electronic flashinstallations, which allow radiation curing without photoinitiator, orexcimer sources. Radiation curing is accomplished by exposure tohigh-energy radiation, i.e., UV radiation or daylight, preferably lightin the wavelength (λ) range of from 200 to 700 nm, more preferably from200 to 500 nm, and very preferably from 250 to 400 nm, or by bombardmentwith high-energy electrons (electron beams; 150 to 300 keV). Examples ofradiation sources used include high-pressure mercury vapor lamps,lasers, pulsed lamps (flash light), halogen lamps, or excimer sources.The radiation dose normally sufficient for crosslinking in the case ofUV curing is in the range from 80 to 3000 mJ/cm².

It is of course also possible to use two or more radiation sources forthe cure, e.g., from two to four.

These sources may also each emit in different wavelength regions.

Irradiation can be carried out where appropriate in the absence ofoxygen as well, such as under an inert gas atmosphere, for example.Suitable inert gases include, preferably, nitrogen, noble gases, carbondioxide or combustion gases. Irradiation may also take place with thecoating material covered with transparent media. Examples of transparentmedia include polymeric films, glass or liquids, such as water.Particular preference is given to irradiation in the manner described inDE-A1 199 57 900.

The invention further provides a method of coating substrates whichcomprises

-   -   i) coating a substrate with a coating material as described        above,    -   ii) removing volatile constituents of the coating material, for        the purpose of forming a film, under conditions in which the        photoinitiator (I) essentially as yet does not form any free        radicals,    -   iii) if desired, irradiating the film formed in step ii) with        high-energy radiation, the film being precured, and then, where        appropriate, machining the article coated with the precured film        or contacting the surface of the precured film with another        substrate,    -   iv) fully curing the film, thermally or with NIR radiation.

Steps iv) and iii) can also be carried out in reverse order, i.e., thefilm can be cured first thermally or by NIR radiation and then withhigh-energy radiation.

The present invention further provides substrates coated with amulticoat paint system of the invention.

The thickness of such a film to be cured as described can be from 0.1 μmup to several mm, preferably from 1 to 2000 μm, more preferably from 5to 1000 μm, very preferably from 10 to 500 μm, and in particular from 10to 250 μm.

The coating materials of the invention are suitable with particularpreference as or in exterior coatings, i.e., those applications whichare exposed to daylight, preferably on buildings or parts of buildings,interior coatings, traffic markings, and coatings on vehicles andaircraft. The coatings are employed in particular as wood, paper orplastics coatings, for woodblock flooring or furniture for example.

The process of the invention allows the preparation of partial(meth)acrylic esters (F) in high chemical and space/time yield and undermild conditions and with good color numbers. Through the use ofprotective groups the desired partially esterified products are obtainedin a targeted way and are free from by-products.

The examples which follow are intended to illustrate the qualities ofthe invention without, however, restricting it.

EXAMPLES

Parts in this document, unless specified otherwise, are to be understoodas referring to parts by weight.

Example 1 Isopropylidene-glycerol+ethyl acrylate (variation of solvent)

5 mmol of 2,3-isopropylidene-glycerol, 50 mmol of ethyl acrylate, 10 mlof solvent and 100 mg of Novozym 435 were shaken at 40° C. for 24 h.

The reaction mixture was filtered and the conversion to2,3-isopropylidene-glycerol monoacrylate was determined by gaschromatography.

Conversion Solvent [%] none 74 acetone 68 1,4-dioxane 74 MTBE 74 toluene74 acetonitrile 74 THF 71 MTBE: methyl tert-butyl ether

MTBE: methyl tert-butyl ether

Example 2 Isopropylidene-glycerol+alkyl acrylate (variation of alkylacrylate)

5 mmol of 2,3-isopropylidene-glycerol (IPG), 25-100 mmol of alkylacrylate and 100 mg of Novozym 435 were shaken at 20, 40 or 60° C. for24 h.

The reaction mixture was filtered and the conversion to2,3-isopropylidene-glycerol monoacrylate was determined by gaschromatography.

Conversion [%] Conversion [%] Conversion [%] Acrylate:IPG with methylwith ethyl with butyl [mol/mol] acrylate acrylate acrylate at 20° C. 5:1 58 65 61  7:1 61 69 67 10:1 67 74 71 10:1 (72 h) 67 74 71 20:1 7683 80 at 40° C.  5:1 60 66 64 10:1 71 76 75 10:1 (72 h) 69 75 73 20:1 7985 84 at 60° C.  5:1 61 67 66 10:1 72 78 76 10:1 (72 h) 72 78 77 20:1 8186 85

Example 3 Isopropylidene-glycerol+methyl acrylate

4.0 mol (528.8 g) of 2,3-isopropylidene-glycerol, 20.0 mol (1722 g) ofmethyl acrylate, 86 mg of phenothiazine, 344 mg of p-methoxyphenol, 800g of molecular sieve (5 Å) and 80.0 g of Novozym 435 were stirred atroom temperature for 24 h in a round-bottomed flask.

The reaction mixture was filtered and the excess methyl acrylate wasremoved on a rotary evaporator. The batch was run twice withreproducible conversions.

Conversion Batch [%] Yield [g] A 93 674.6 B 94 724.1

For the hydrolysis of the isopropylidene group, 680 g of2,3-isopropylidene-glycerol monoacrylate were stirred with 680 g ofwater and 68 g of strongly acidic ion exchanger (Dowex 50 Wx8H⁺ form) atroom temperature for 24 h. The ion exchanger was removed by filtrationand the acetone formed was removed under reduced pressure on a rotaryevaporator at 20-30° C.

The resultant aqueous solution of glycerol monoacrylate can be usedfurther directly for the copolymerization. According to the analysis byGC the organic fractions of the solution are composed of 94.3% glycerolmonoacrylate, 5.2% glycerol, and 0.5% 2,3-isopropylidene-glycerolmonoacryate.

As an alternative it is possible to prepare an anhydrous product byextracting the aqueous solution with ethyl acetate, drying the extractover sodium sulfate, and freeing it from ethyl acetate again on a rotaryevaporator. The anhydrous, colorless oil is composed according toanalysis by GC of 97.1% glycerol monoacrylate, 1.9% glycerol, 0.6%2,3-isopropylidene-glycerol monoacrylate, and 0.3%2,3-isopropylidene-glycerol.

Example 4 2,3-Isopropylidene-glycerol+methyl acrylate

In a round-bottomed flask 0.1 mol (13.2 g) of2,3-isopropylidene-glycerol, 1 mol (86.1 g) of methyl acrylate and 650mg of Novozym 435 were stirred at 60° C. under reduced pressure (450-470mbar). The vapor (methyl acrylate+methanol) was passed in a tube into acondenser. The condensate dripped back into the reaction mixture via adropping funnel filled with 20 g of molecular sieve (5 Å). After 6 h asample was taken from the mixture and the conversion was determined bymeans of GC to 99.5%.

Example 5 2,3-Isopropylidene-glycerol+methyl methacrylate

5 mmol of 2,3-isopropylidene-glycerol (IPG), 10-50 mmol of methylmethacrylate (MMA), 1.0 g of molecular sieve (5 Å) and 100 mg of Novozym435 were shaken at 20 or 40° C. for 24 h.

The reaction mixture was filtered and the conversion to2,3-isopropylidene-glycerol monomethacrylate was determined by gaschromatography.

Conversion Conversion MMA:IPG [%] [%] [mol:mol] at 20° C. at 40° C. 2:178 91 3:1 78 89 5:1 90 90 7:1 92 94 10:1  91 95

Example 6 Isopropylidene-protected trimethylolpropane+methyl acrylate

5 mmol of isopropylidene-trimethylolpropane (IPT), 10-50 mmol of methylacrylate (MA), 1.0 g of molecular sieve (5 Å), optionally 10 ml ofmethyl tert-butyl ether (MTBE) and 100 mg of Novozym 435 were shaken at20, 40 or 60° C. for 24 or 72 h. The reaction mixture was filtered andthe conversion to isopropylidene-trimethylolpropane monoacrylate wasdetermined by gas chromatography.

Reactions without MTBE Conversion Conversion Conversion MA:IPT [%] [%][%] [mol:mol] at 20° C. at 40° C. at 60° C.  2:1 (24 h) 14 20 19  5:1(24 h) 14 16 22 10:1 (24 h) 11 16 16 10:1 (72 h) 14 21 — Reactions withMTBE Conversion Conversion MA:IPT [%] [%] [mol:mol] at 20° C. at 40° C. 2:1 (24 h) 10 21  5:1 (24 h) 11 19 10:1 (24 h)  9 17 10:1 (72 h)  8 21

Example 7 Isopropylidene-glucofuranose+methyl acrylate

5 mmol of isopropylidene-glucofuranose (IP-Glu), 50 mmol of methylacrylate (MA), optionally 1.0 g of molecular sieve (5 Å), optionally 10ml of solvent, and 100 mg of Novozym 435 were shaken at 40° C. for 24 h.

The reaction mixture was filtered and the conversion toisopropylidene-glucofuranose monoacrylate was determined by gaschromatography.

Conversion Conversion [%] [%] without with molecular molecular Solventsieve sieve none 53 85 Acetone 51 73 1,4-dioxane 54 80 THF 52 68

1. An enzymatic method for preparing (meth)acrylic esters ofpolyalcohols comprising at least one selected from the group consistingof: esterifying a (meth)acrylic acid with a protected polyalcohol in thepresence of at least one enzyme, and transesterifying at least one(meth)acrylic ester of a saturated alcohol with a protected polyalcoholin the presence of at least one enzyme; wherein the protectedpolyalcohol is a polyalcohol wherein at least two hydroxyl groups arejoined in an acetal or ketal group, and at least 70% of all hydroxylgroups of the protected polyalcohol are converted to (meth)acrylic esterof protected polyalcohol.
 2. The process according to claim 1, whereinthe at least one (meth)acrylic ester of a saturated alcohol is asaturated C₁-C₁₀-alkyl (meth)acrylate.
 3. The process according to claim1, wherein the the protected polyalcohol is obtained by a) reacting analdehyde or ketone with a polyalcohol and b) optionally, purifying thereaction mixture obtained from a), wherein the aldehyde or ketone isrepresented by the formula IR¹—C(═O)—R²  (I), where radicals R¹and R² independently of one anotherare hydrogen, C₁-C₁₈ alkyl, C₂-C₁₈ alkyl uninterrupted or interrupted byone or more oxygen and/or sulfur atoms and/or by one or more substitutedor unsubstituted imino groups, or are C₂-C₁₈ alkenyl, C₆-C₁₂ aryl,C₅-C₁₂ cycloalkyl or a five- or six-membered, oxygen-, nitrogen- and/orsulfur-containing heterocycle, and wherein the specified radicals may besubstituted in each case by aryl, alkyl, aryloxy, alkyloxy, heteroatomsand/or heterocycles or for R¹ and R² together with the carbonyl carbonto form a four- to twelve-membered ring, and the polyalcohol has from 3to 10 hydroxyl groups.
 4. The process according to claim 1, wherein theprotected polyalcohol comprises a 1,3-dioxolane or 1,3-dioxane structurewhich is mono- or disubstituted in position
 2. 5. The process accordingto claim 4, wherein the the protected polyalcohol is at least oneselected from the group consisting of4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane,4-hydroxymethyl-2-methyl-1,3-dioxolane,4-hydroxymethyl-2,2-diethyl-1,3-dioxolane,4-hydroxymethyl-2-tert-butyl-1,3-dioxolane,4-hydroxymethyl-2-phenyl-1,3-dioxolane,5-ethyl-5-hydroxymethyl-2,2-dimethyl-1,3-dioxane,5-ethyl-5-hydroxymethyl-2-methyl-1,3-dioxane,5-ethyl-5-hydroxymethyl-2,2-diethyl-1,3-dioxane,5-ethyl-5-hydroxymethyl-2-tert-butyl-1,3-dioxane,5-ethyl-5-hydroxymethyl-2-phenyl-1,3-dioxane,1,2-O-isopropylidene-α-D-glucofuranose, 2,3-O-isopropylidene-threitol(=2,2-dimethyl-1,3-dioxolane-4,5-dimethanol),5,5-bis(hydroxymethyl)-2,2-dimethyl-1,3-dioxane and mixtures thereof. 6.The process according to claim 1, wherein the reaction mixture from theesterifying or the transesterifying is purified.
 7. The processaccording to claim 1, wherein the reaction mixture from the esterifyingor the transesterifying is deprotected and, optionally, purified.
 8. Theprocess according to claim 1, wherein the enzyme is at least oneselected from the group consisting of esterases (E.C. 3.1.-.-), lipases(E.C. 3.1.1.3), glycosylases (E.C. 3.2.-.-), and proteases (E.C.3.4.-.-).
 9. The process according to claim 6, wherein the purifiedreaction mixture from the esterifying or the transesterifying isdeprotected and, optionally, further purified.